I got some time to start working this up tonight. This is far from compete but shows a possible configuration of the inner structure that provides linear motion. I haven't gotten around to doing the drives yet and the extruder mount will be reworked... this was just an extruder setup I had laying around so I tossed it in for show. There will be an outer skeleton that the skins attach to. All the electronics will be mounted internally as well as the wiring. Filament spools will be in refillable cartridges that attach to the rear and provide moisture protection. The extruders will use bowden connections. The large opening in the front will have a see-through door. The build platform, I'm thinking, will be a piece of tempered glass with kapton covering and will be removable. Build area is 400x800x400mm (trying to make it as big as possible and still fit on my side desk).

The little clear container on the left side will have wipers on it for cleaning the hotends when filaments are changed during printing.

Looks like the max operating temp for the delrin wheels is about 80 deg C... if this proves to be too low for reliable adhesion (never tried an enclosure before but it's on the low side for ABS in the open) I'll add provision for a heated platform to boost the local temp on the bed a bit.

I don't have the software to check the beam deflection on these 800mm+ lengths ... I'll figure that out at some point... I guess I could calculate it by hand. If anyone knows what to expect with various loads that would be awesome.

I didn't add it yet but I was thinking of making the print bed frame float on the z axis carriages. To your point though, if I keep it rigid then maybe I could just treat the entire thing as one carriage and remove the inner wheels? Or, Frederic, were you suggesting that I just have three wheels per z axis carriage (like the ORD Bot) rather than the four I'm showing?

I never had issues aligning the Z axis on my ORD Bot, but I took a lot of time and used multiple machinist squares to get it perfect. I was expecting this box frame to be harder to get true and was hoping that the cross braces would aid in that.

Quite a bit larger than a rigidbot. Also considerably more feature-packed. And at this rate I I'll have mine sooner than the rigidbot backers.

And on the naming topic... in my 16 years of product development we always name our long-term efforts at the start. Helps make it real. I think I'm going to skip the ORD moniker since this thing has nothing to do with the Google conference. I'd thought for a second of calling it the Vapor Bot in honor of orcinus... but instead I'm going to call it the Joggle Bot. Don't ask me why ... I just love the Wikipedia image of the dude joggling.

I incorporated the floating bed mounts tonight to address the over constraint issue Frederic pointed out; all the z axes are decoupled now. The print bed now simply rests on top of some pivot blocks that will forgive a bit of misalignment in the build. I'll refine these blocks more to allow for fine height adjustment to help with leveling the bed. I also worked up the ball nut screws to drive the z axis. These screws are 5mm/turn so with the 1.8 degree stepper running full steps I can hit my 100 micron height target with four full steps. No microsteps required... nice and even. This pic shows the floating mounts:

Also for fun I did this render showing the size difference between the Joggle Bot and the ORD Bot Hadron. This is just the inner frame too, I still need to add the outer skins for the heat chamber.